code: def test_preconditioner(self):
      # Check that preconditioning works
      pc = splu(Am.tocsc())
      M = LinearOperator(matvec=pc.solve, shape=A.shape, dtype=A.dtype)
  
      x0, count_0 = do_solve()
      x1, count_1 = do_solve(M=M)
  
      assert_equal(count_1, 3)
      assert_(count_1 < count_0 / 2)
      assert_(allclose(x1, x0, rtol=1e-14))
  
file_path: scipy/scipy/sparse/linalg/_isolve/tests/test_gcrotmk.py
imports: from numpy.testing import assert_, assert_allclose, assert_equal, suppress_warnings
  import numpy
  from numpy import zeros, array, allclose
  from scipy.linalg import norm
  from scipy.sparse import csr_matrix, eye, rand
  from scipy.sparse.linalg._interface import LinearOperator
  from scipy.sparse.linalg import splu
  from scipy.sparse.linalg._isolve import gcrotmk, gmres
label_desc: Use image node_id 1 for calling the TestGCROTMK obj's underlying member method code with example usage: obj.test_preconditioner() without return types